One of the inspirations for the film was the real WWII sharpshooter Simo Häyhä who fought against the Red Army and who is believed to have killed over 500 enemy soldiers during the Winter War, which is why he is often regarded as the deadliest sniper of all time, known as the "White Death."
The actors by and large insisted on doing their own stunts.
The exteriors are shot in Finnish Lapland, mainly near the villages of Nuorgam and Kaamanen in the Utsjoki municipality.
Jalmari Helander was originally going to direct a comedic sci-fi film "Jerry and Ms Universe" in Canada as his next project after La gran aventura (2014). When it was postponed due to the COVID-19 pandemic, he quickly wrote Sisu (2022) in the fall of 2021. The film's budget was $6.5 million.
"Sisu" is a Finnish word described as stoic determination, grit, bravery, resilience, and hardiness.